For the first time in an incredibly long time, new titles are being added to the Public Domain in the United States!
On January 1, 2019, the provisions set forth in the Copyright Extension Act of 1998 finally expires, allowing hundreds of works to enter the Public Domain. From here on out (barring another piece of legislation to the contrary), new works will enter the Public Domain on January 1 of each year, just as they do in other countries.
This year, it means that works published before 1924 (with some exceptions) are now open for use without gaining permission from the author, their agent, or estate. So, works like Robert Frost's collection of poems New Hampshire will be available for use, as will the film The Ten Commandments (the Cecil B. DeMille version, anyway).
While it's true that some works published in 1923 (and later) might already have been in the public domain if copyright was improperly registered or renewed, and conversely, a (very) few works may still remain under copyright, it remains important to conduct the proper research into the copyright status of a work prior to using it.
But for now, authors, artists, filmmakers, and really anyone is free to create their own editions, versions, translations, or adaptations of works from 1923 and before. Hooray for more creative endeavors!